Oscillation Circuit with Fast Frequency Locking via Time-to-Digital Control
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Solution Overview
Problem
Semiconductor integrated circuits face challenges in quickly locking clock signal frequencies, as ring oscillators take microseconds to milliseconds to stabilize, and CR oscillators are limited in generating high-frequency signals due to low frequency accuracy.
Innovation Solution
The oscillation circuit employs a voltage generator, comparators, a time-to-digital converter, and a ring oscillator with a delay circuit and phase detector to generate a high-frequency oscillation signal by comparing linearly changing voltage with reference voltages, allowing for rapid frequency locking without an external reference clock.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a ring oscillator is used to generate clock signals, then the circuit can operate at high frequencies, but the lock time becomes excessively long (microseconds to milliseconds)
Solution Approach 1:
The patent applies preliminary action by pre-charging the capacitor to a voltage higher than the reference voltage before oscillation starts. When the oscillation enable signal is activated, the capacitor voltage immediately exceeds the reference voltage, causing the first comparator to output a high signal right away. This preliminary preparation eliminates the startup delay normally required for the oscillator to reach stable operation, achieving rapid frequency locking while maintaining high oscillation frequencies.
2Loss of time
If a CR oscillator is used to shorten lock time, then the response speed improves, but the frequency accuracy deteriorates making it suitable only for low-frequency signals
Solution Approach 1:
The patent introduces an intermediary mechanism consisting of the pre-charged capacitor and comparator-based control system. Instead of relying on the slow natural charging process of a CR oscillator, the system uses the pre-charged capacitor as an intermediary energy storage element that can instantly provide the voltage needed to start oscillation. The comparators act as intermediaries to detect and control the oscillation state, enabling rapid frequency locking with high accuracy by controlling the number of delay circuit stages based on the oscillation enable signal, thus achieving both fast response and high frequency accuracy.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the number of delay circuit stages connected in the ring oscillator based on the oscillation enable signal. When oscillation is enabled, the system configures the delay circuit with an appropriate number of stages to achieve the desired frequency and accuracy. This dynamic parameter adjustment allows the oscillator to operate at high frequencies with high accuracy, overcoming the limitation of CR oscillators which are restricted to low frequencies due to their inherent inaccuracy.
3Productivity
If the oscillation frequency is increased to achieve high-speed transmission, then the data rate improves, but the circuit becomes more sensitive to manufacturing process, power supply, and temperature variations
Solution Approach 1:
The patent implements feedback through the comparator-based control system that continuously monitors the oscillator's operation. The first comparator compares the capacitor voltage with the reference voltage to detect the oscillation state, and the second comparator provides additional feedback for stability control. This feedback mechanism allows the system to maintain stable oscillation frequency even at high speeds by automatically adjusting to variations caused by manufacturing processes, power supply fluctuations, and temperature changes, thus improving frequency stability while maintaining high data transmission rates.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables the generation of a high-frequency oscillation signal that can be promptly locked, suitable for high-speed transmission applications, with the oscillation frequency being adjustable and less prone to manufacturing process, power supply, and temperature variations.
Implementation Method 1
a voltage generator 2, which generates a linearly changing voltage
Implementation Method 2
a first comparator 3, which compares a linearly changing voltage generated by the voltage generator 2 with a first reference voltage VREF1, and outputs a signal indicating a comparison result
Implementation Method 3
a time-to-digital converter 6, which converts a time difference between a time point at which an output signal from the first comparator 3 changes from a low level to a high level and a time point at which an output signal from the second comparator 4 changes from a low level to a high level, into a bit sequence signal
Implementation Method 4
an oscillator 7, which generates an oscillation signal based on the bit sequence signal outputted from the time-to-digital converter 6
Data Source
AI summary
An oscillation circuit has a voltage generator configured to generate a linearly changing voltage, a voltage level of which linearly changes as time passes, a first comparator configured to compare the linearly changing voltage with a first reference voltage, a second comparator configured to compare the linearly changing voltage with a second reference voltage having a higher voltage level than the first reference voltage, a time-to-digital converter configured to output a bit sequence signal in accordance with a time difference between a time when the first comparator detects that the linearly changing voltage matches the first reference voltage and a time when the second comparator detects that the linearly changing voltage matches the second reference voltage, and an oscillator configured to generate an oscillation signal that oscillates at a frequency according to the bit sequence signal.